Tough to prove

puzzling Cancer is caused by an accumulation of genetic mutations – tiny distortions in a cell’s DNA that retool it into a vicious replicating machine. But can cancer be caused by external environment agents, asks George Johnson

Recently, thousands of Marines and their families were blocked in federal court in US from
pursuing their claim that the government had given them cancer. The decision, involving people
exposed to contaminated drinking water while stationed at Camp Lejeune, a base in North Carolina, did not consider the science. Long before expert witnesses could be called to testify, a US Court of Appeals let stand its earlier ruling that the lawsuit had come too late. It failed to meet the requirements of a state statute banning claims arising more than 10 years after the final occurrence of a harmful act.

The genetic mutations that cause cancer can take decades to manifest themselves, far longer than the North Carolina statute of repose allowed. But the laws we cobble together often trump those of science. And even when legal obstacles can be overcome, a link between a cancer and environmental pollutants is exceedingly difficult to establish, whether in a laboratory or a court of law. In past
investigations, only two residential cancer clusters in the country have been linked, though only weakly, to environmental toxins. Camp Lejeune has become the third. The plaintiffs in the lawsuit lived at the base at various times from the 1950s through 1985, a period when the drinking water was polluted with dry-cleaning fluid, organic solvents and benzene – chemicals on the National Toxicology Programme’s list of known and probable carcinogens.

Numbers speak
Even so, epidemiological studies published last year by the Centers for Disease Control and Prevention found that Camp Lejeune’s rate of cancer mortality was lower than that of the general public – 1,078 cases among the Marines during a 10-year period, when 1,272 would have been expected in a population that size. That would ordinarily seem to rule out a cancer cluster. Epidemiologists, however, suspected that the numbers might have been distorted by a “healthy soldier” or “healthy veteran” effect.

The military and their kin may receive better medical care than most people, making them less likely to die prematurely from cancer. To allow for that possibility, cancer deaths at Camp Lejeune were compared with those at Camp Pendleton in Southern California, where there was no water contamination. It was then that hints of a problem appeared. Overall, Marines who had served at
Lejeune were 10 per cent more likely to die from cancer than their counterparts at Pendleton.

Deaths from kidney cancer, for example, were 35 per cent more likely. Altogether, 16 of 21 types of cancer showed modest increases at Lejeune. Most of these conditions are rare enough that the
absolute number of excess deaths was low – 42 from kidney cancer, for example, when 36 was considered average. For multiple myeloma, the increased risk was razor thin: 17 deaths at Lejeune, when 16 would have been expected. (Similar results were found in a separate study involving the base’s civilians.)

The more unusual a cancer, the harder it is to separate genuine influences from statistical noise. Especially puzzling were some 80 Lejeune veterans who came forward with diagnoses of male breast cancer, some at an unusually early age. The annual incidence of this condition is about 1.4 cases per 1,00,000 men – about 1 per cent of the rate for women. Hundreds of thousands of men may have been exposed, for various lengths of time, to Camp Lejeune water. Whether that is enough to implicate the pollution is still under consideration.

Investigations of other suspected cancer outbreaks have been even less clear-cut. Over the years, state and federal epidemiologists have looked into hundreds of incidents in which people have reported what they feared were unusually high concentrations of cancer. Only a fraction of these turned out to be genuine anomalies, with cancer rates that were actually higher than demographics would suggest.

Of these outliers, only two were ultimately associated with an environmental agent. The rest of the clusters apparently occurred by chance, like stars forming constellations in the sky.
Among the places that didn’t make the cut were Love Canal, New York, which was the original Superfund site, and Hinkley, California, the subject of the movie Erin Brockovich.

Clusters involving factory workers are more common – the exposures are more intense. But you can scour the records and find only two cases in recent history in which environmental contaminants may have caused a blip in the cancer rate: a small increase in the number of childhood leukemias in Woburn, Massachusetts,

featured in the movie A Civil Action, and in Toms River, New Jersey.In both investigations, a wisp of a pattern emerged when the data was parsed just so. In Woburn, a few extra cases occurred among boys, and in Toms River among girls. Nothing known about the biology of leukemia could
explain why the carcinogens in question would have exhibited a preference for
gender, leading to doubts that the clusters were real.

Biologists tell us that cancer is caused by an accumulation of genetic mutations -–tiny distortions in a cell’s DNA that retool it into a viciously replicating machine. Some of the mutations are inherited, some are inflicted by outside agents, and some are simply copying errors that occur
spontaneously as a body’s cells divide. Pollutants add to the burden.

But no matter how carcinogenic they are, the doses most people receive can hardly compare with the thick concentration of chemical waste inhaled, minute after minute, by cigarette smokers into the microscopic depths of their lungs. To get that kind of exposure, you would have to hook a tube to a factory smokestack and breath the fumes for years, or subject yourself to an intravenous drip of toxic sludge. None of this means that the spillage of manufactured chemicals is not a problem or that polluters should not be fined and jailed.

Some epidemiologists suspect that synthetic carcinogens are giving many people cancer, but at levels that their mathematical tools cannot detect. Judging from the evidence, the former residents of Camp Lejeune may have a stronger argument than the people of Woburn and Toms River did, but only if their lawyers can find a way to get the case back into court.